Multiple sclerosis (MS) is the most common demyelinating disease of humans. Although its cause is unknown, clues to the nature of disease may be found in the increased IgG and oligoclonal bands (OGBs) present in the CSF and brain of MS patients, an phenomenon almost exclusively seen with infectious and inflammatory diseases of the CNS. Although the specificity of OGBs in MS is unknown, in infectious diseases of the CNS, OGBs are specific for the agent that causes disease, thus providing a rationale for our hypothesis that OGBs in MS brain and CSF are directed against the antigen that causes disease. In the past funding period, analysis of the lgG heavy (VH) and light (VL) chain variable region sequences expressed in acute MS brains and CSFs revealed a restricted IgG repertoire indicative of an antigen-driven B cell response. To produce recombinant antibodies from prominent MS Ig sequences that accurately duplicate the B cell heavy- and light- antibody chain pairings found in vivo, we developed an RT-PCR protocol to amplify the expressed V-region sequences of single B cells and plasma cells isolated from MS CSF by fluorescence-activated cell sorting. The paired heavy and light chains from CSF clonal B cell populations will now be used to produce a panel of recombinant mAbs whose specificity will be determined. Once specificity is established, cDNAs whose protein products react with MS-specific Abs will be cloned and characterized. Also, to better understand the dynamics of the B cell response in MS and to further characterize the nature of the humoral response in MS, changes in the IgG repertoire of MS CSF with disease progression will be analyzed. We are well-prepared to conduct these studies because we have: (a) a well-characterized pool of CSF from MS patients and patients with other CNS inflammatory disease; (b) a demonstrated ability to amplify disease-relevant IgG sequences from human CSF and brain, and to use these sequences to generate recombinant IgG; and (c) the expertise in molecular biology and immunology to identify the antigenic target of the recombinant Abs. Identification of an MS-specific antigen(s) will have wide application, not only for early definitive diagnosis, but also for developing strategies to modulate and possibly prevent disease.